1. Field of the Invention
The present invention relates to a method for detecting a replacement of sheathed-element glow plugs in an internal combustion engine, in which at least one electrical parameter of the sheathed-element glow plug is determined during a driving cycle and is compared with a stored value of the same electrical parameter of the sheathed-element glow plug that was determined in a preceding driving cycle; and to an apparatus for carrying out the method.
2. Description of the Related Art
Published German patent application document DE 10 2008 007 398 A1 discloses a method and an apparatus for detecting the replacement of sheathed-element glow plugs in an internal combustion engine, in which, at the beginning of a driving cycle, at least one electrical characteristic value of at least one sheathed-element glow plug is measured, a present value of that characteristic value is determined and is compared with at least one stored value of the same electrical characteristic value of that sheathed-element glow plug that was determined at the beginning of at least one preceding driving cycle, and in which, if the deviation of the present value from the stored value exceeds a predefinable threshold value, a plug replacement is detected. Current, resistance, and/or electrical-power profiles or individual defined values are utilized for an individual-plug evaluation of this kind, by the fact that these profiles and/or values from the present driving cycle and the preceding one are compared. Because these individual-plug current, resistance, and/or electrical-power profiles greatly depend on environmental conditions, it is difficult always to evaluate them accurately, since the environmental conditions cannot always necessarily be set identically in the various driving cycles.
These individual current, resistance, and electrical-power profiles and/or values of each sheathed-element glow plug depend on the age of the plug, on environmental conditions (engine operating conditions), and on the applied voltage. These differences exist for sheathed-element glow plugs of identical type.